body {
    font-family: Arial, sans-serif;
}

.container {
    width: 90%;
    max-width: 600px;
    margin: 30px auto;
    text-align: center;
}

input[type="text"] {
    width: 70%;
    padding: 10px;
    margin-right: 10px;
}

button {
    padding: 10px;
}

ul {
    list-style-type: none;
    padding: 0;
}

li {
    margin-top: 10px;
    background-color: #f4f4f4;
    padding: 10px;
    cursor: pointer;
}

li.completed {
    text-decoration: line-through;
}